Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 65: Oxides and Insulators

O 65.5: Poster

Wednesday, March 18, 2015, 18:15–21:00, Poster A

Fine structure in infrared spectra of high quality CO₂ ultrathin films on the NaCl(100) surface — •Jochen Vogt — Chemisches Institut der Uni Magdeburg, Magdeburg, Germany

The splitting of the ν₃ asymmetric stretch mode into a longitudinal optical (LO) and a transverse optical mode (TO) is a well known feature of CO₂ ice thin films [1]. In new experiments, high quality ultrathin films were grown by exposure of a saturated monolayer CO₂-p(2×1)/NaCl(100) to additional CO₂ at 40 K. Films prepared in this way appear to be highly ordered over a wide spatial range and show additional fine structure between the TO and LO modes. A mode at 2348.9 cm⁻¹ is observed in p- and s-polarized spectra and does not shift with increasing film thickness. According to a simulation of the film spectra based on vibrational exciton theory, this mode can be assigned to a collective vibrational excitation of molecules near the interface with the substrate. Additional peaks e. g. at 2359.1 cm⁻¹ and 2363.8 cm⁻¹ show up and disappear again during film growth. These modes can be assigned to resonant excitation of domains with unique film thickness. [1] O. Berg, R. Disselkamp, G. E. Ewing, Surf. Sci. 277 (1992), 8.